The ability to metastase forms the actual life-endangering property of malignant tumour cells. The original primary tumour cells probably acquire this property by a whole series of changes in the course of the tumour progression. As a result of this process, cancer cell variants are continuously detached from the primary tumour mass, penetrate the extracellular matrix and migrate into the lymphatic system or the blood circulation. Often adhering to one another, the metastasing tumour cells are transported in the blood or lymph system, leave the vascular system at other places in order there to penetrate into secondary tissue and form daughter tumours (survey of Hart et al., 1989; Nicolson, 1987). The formation of metastases requires a whole series of interactions of the tumour cells with intercellular matrix and other cells. Almost all of these interactions require cell surface components, such as e.g. the receptors for matrix and lamina, surface-bound proteolytic enzymes, as well as cell adhesion molecules with inclusion of those which cause organ-specific adhesion and thus organ preference of the metastasis, furthermore growth factors and growth factor receptors.
It is known that the membrane proteins differentiate non-metastasing and metastasing tumour cells of the BSp73 rat tumours, demonstrated by antibody reaction (Matzku et al., 1983 and 1989).